This invention relates to thin film magnetic heads, and more particularly relates to a composite structure including a substantially single domain magnetic element, a method of producing such a structure and thin film magnetic heads incorporating such a structure.
Thin film magnetic heads are being developed which offer the advantages of miniaturization and integration on a single substrate. In the case of magnetic tape, information is written onto, and read from, spaced, parallel tracks on the tape. To increase information density, the width of the tracks, as well as the spacing between the tracks, can be reduced. For example, in the newly proposed format for digital (audio) compact cassettes (dcc), there are a total of 18 separate, parallel tracks on a tape having the same width as the conventional compact cassette.
In order to achieve magnetic heads having correspondingly small dimensions, such heads are now being developed using thin film processing techniques of the type used to manufacture integrated circuits in silicon substrates.
In order to achieve track alignment between the read and write magnetic heads, it has been proposed that the read and write heads be integrally combined in a unitary structure. See, for example, parent U.S. patent application Ser. No. 703,539 (PHA 21,669), filed May 21, 1991, and assigned to the present Assignee, in which a combined read/write magnetic head is disclosed in which the read head includes a magnetoresistive element (MRE) overlying a substrate of substantially magnetically impermeable material, a broken (discontinuous) flux guide overlying the MRE and a continuous flux guide overlying the broken flux guide. The write head of the combined read/write magnetic head overlies the read head and shares the continuous flux guide with the read head, the continuous flux guide serving as a bottom pole of the write head. Significantly, the dimensions of the various elements of the combined read/write magnetic head are chosen so that relatively little magnetic flux produced by the write head during writing, or entering the write head during reading, is communicated via the shared flux guide to the MRE.
The successful operation of such a device depends on the MRE of the read head being a substantially single domain element. The ability to deposit such an element requires a smooth, preferably stress-free substrate surface. Otherwise, surface irregularities can form pinning sites for the formation of domain wall boundaries.
In U.S. Pat. No. 4,608,293, a magnetic layer is formed on an insulating oxide layer after the surface of the oxide layer has been carefully polished under pressure using a rotating polisher in a suspension in pure water of MgO, SiO.sub.2 or Al.sub.2 O.sub.3 powder or a mixture thereof having a particle diameter not exceeding 0.1 micron.
However, such a polishing techinque leaves surface scratches which can act as pinning sites for the formation of domain wall boundaries.